The present disclosure relates to a battery pack having a cooling structure with improved stability for use of a liquid coolant.
Recently, a chargeable and dischargeable secondary battery is widely used as an energy source for wireless mobile devices. Further, a secondary battery also attracts attention as a power source for an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (Plug-In HEV) and the like that are suggested as an alternative to solve air pollution caused by conventional gasoline vehicles and diesel vehicles that are operated on fossil fuel.
While one, two, three or four battery cells are used per one device in compact mobile devices, a battery module in which multiple battery cells are modularized, or a battery pack in which multiple battery modules are electrically connected is used in medium/large-sized devices such as a vehicle for the necessity of high-output power and large-capacity.
Since a medium/large-sized battery module or battery pack is preferably manufactured with as small size and weight as possible, a prismatic battery, a pouch-shaped battery, and the like, which can be laminated with high degree of integration and have small weight to capacity are mainly used as battery cells (unit cell) thereof. Particularly, the pouch-shaped battery using an aluminum laminate sheet as a sheathing member has recently attracted a lot of attention owing to advantages such as low weight, low manufactured cost, and easy deformable properties.
Since battery cells constituting such medium-to-large size battery module or battery pack are composed of chargeable and dischargeable secondary batteries, such high-output large-capacity secondary batteries generate a large amount of heat during a charging and discharging process. Particularly, since the laminate sheet of the pouch-shaped battery is surface-coated with a polymer material having low thermal conductivity, it is difficult to effectively cool the temperature of the entire battery cell.
If the heat generated during the charging and discharging process cannot be effectively removed, heat build-up may occur, thereby accelerating deterioration of the battery cells and possibly causing ignition or explosion thereof depending on cases. Thus, the high-output large-capacity battery module or battery pack requires a cooling system to cool battery cells stored therein.
Such cooling system may largely be configured in a structure of cooling the unit cells included in the battery pack or the unit battery module, or in a structure that a liquid coolant cools the unit battery cell or the unit battery module while moving along a pipe.
Particularly, the cooling system using the liquid coolant is such that the liquid coolant circulates along the pipe, but may absorb the heat of unit battery cells or unit battery modules adjacent to the pipe, thereby accomplishing cooling, and it may be defined as an indirect cooling system in a broad meaning.
Although such cooling system using the liquid coolant has an advantage in that cooling efficiency is excellent, it may incur critical safety problem to the battery pack when the liquid coolant flows out, and therefore it is necessary to design the cooling structure with a very high degree of precision.
Nonetheless, some of the liquid coolant may flow out through joints of the pipes due to fluid pressure of the liquid coolant, and the so outflowed liquid coolant may infiltrate into the unit battery cell, unit battery module, or circuit that constitutes the battery pack to lead to electrical short-circuit, malfunction, and the like.
In some cases, hot air inside the battery pack may be condensed on the pipe surface, and for this reason, the cooling system using a liquid coolant is particularly required to have the safety against moisture.
Therefore, there is a great need for a battery pack having a cooling structure with improved stability for use of liquid coolant.